Automatic control system



J ne 10, 1941. A. s. NQRRQSS 2,244,722

-AUTOMATIC CONTROL SYSTEM Filed 001;. 21, 1937 2 Sheets-$heet 1 INVENTORAustin 5. Nor-crass BY fw M ATTORNEYS June 10, 1941. A. s. NORCROSSAUTOMATIC CONTROL SYSTEM Filed Oct. 21. 1937 2 Sheets-Sheet 2 ES Q as umE. 5;

INVENTOR Austin .5. Norcro BY pd. M v

ATTORNEYS Patented June 10, 1941' UNITED STATES PATENT OFFICE 19Clailnl.

This invention relates to an automatic control system for regulating themovements oi a regulating device to maintain a condition to becontrolled at a substantially uniform value.

The general object is to provide a control a system oi the abovecharacter which is applicable to the control oi a wide variety oiconditions, which is reliable in operation, which is extremely sensitivedue to the use oi a vacuum tube circuit ior detecting changes in thecontrolled condition, which may be adapted quickly and conveniently tochanges in the character oi the controlled medium and which may beadapted ior use alternatively with a manually operable control. p

A more detailed object is to provide a control system oi the abovecharacter having a vacuum tube control circuit ior measuring variationsin the condition being controlled and a novel means oi modiiying theaction im the control circuit so as to position the regulating devicewith a so-called proportioning action.

Another object is to provide a novel arrangement ior iacilitatingtesting and adjustment oi a control oi the above character.

A'iurther object is to combine a manual control with the automaticcontrol and provide auto- .matically acting means for disabling theautomatic control mechanism while the manual control is in use. 7

Still another object is to provide a novel arrangement by which therange of the proportioning action may be varied selectively withoutdestroying the adjustment oi the control as a whole.

Other objects and advantages oi the invention will become apparent fromthe iollowing detailed description taken in connection with theaccompanying drawings, in whichl'igure 1 is an eievational viewpartially broken away oi a drying apparatm equipped with a control thepresent invention.

Fig. 2 is a plan view.

Fig. 3 is a iragmentary perspective view oi a part of the controlsystem.

Fig.4isaschematicviewandwiringdiagram.

The invention is applicable to the control oivariouskindsoiregulatingdevieessuchas valves, dampers, speed changers,etc. ior regulating a wide variety oi conditions to be controlled. Forpurposes illustration, however, the invention is shown in the drawinlsand will be described herein as applied to the control oi dryingapparatus ior maintaining a uniiorm moisture content in a traveling weboi cloth or the like. I do not intend to limit the invention by suchdisclosure but aim to cover all modifications and alternative methods,constructions,

and uses falling within the spirit and scope oi the invention asexpressed in the appended claims.

The controlled apparatus shown is oi the type commonly known as a tenterand employed ior drying a traveling web 5 of cloth or the like afterfinal washing thereoi. The tenter comprises a housing 6 providing anelonmted chamber 'I through which the web is ied from a wet roll 8 atone end oi the chamber to a dry roll 9 at the opposite end. The web isadvanced though the drying chamber by endless belts ll carrying suitableclamps indicated diagrammatically at ll ior gripping opposite side edgesoi the web to hold it taut. Preierably, the belt sprockets I! are drivenby an electric motor ll operating through suitable speed reducingmechanism indicated at I4.

Air ior drying the cloth is heated by means such as a coil i5 suppliedwith steam or other heating medium and preferably maintained at auniform temperature by means such as a thermostatically controlled valveIt. Byoperation of a power driven blower il, air is iorced through theheater and then through the chamber 1 in a direction reverse to themovement of the web 5. By varying the rate oi travel of the web, thetemperature oi the heater it or the volume oi air flowing through thechamber, the drying capacity oi the tenter, that is, the ability toreduce the moisture content oi the dried cloth as it passes through thechamber I, may be regulated. In the present instance. such regulation iseiiected by varying the speed of the motor I! which ior this purpose isoi the so-calied shunt type having its field winding ll (Fig. 4) adaptedto be energized to a predetermined degree from a source oi directcurrent and its armature II variably energized to determine the motorspeed.

Control oi the motor speed is eii'ected in the present instance by arheostat 20 arranged to vary the current in the motor armature circuitin accordance with changes in the position oi the rheostat arm Ii whichconstitutes the movable regulating member irthe present control system.

Herein the arm II is arranged to be oscillated varying distances backand iorth across the resistance element 22 oi the rheostat by anelectric motor 23 operating through speed reduction gearing 24 to drivea shait 2' on which the arm 2| is fast, Preferably, the motor 23 is ofthe shaded pole induction type having a winding 26 normally energizedfrom a source of alternating current and a squirrel cage rotor 28arranged to turn clockwise and counter-clockwise respectively accordingto which of two sets of shading coils 28 and 30 is short-circuited, therotor remaining idle when both coils are opencircuited. Operation of themotor 23 is controlled by two switches 3| and 32 having a common contact33 connected by a conductor 34 to the common terminal of the shadingcoils. The insulated terminals of the respective coils 28 and 30 areconnected by conductors 35 and 35 to the stationary contacts of theswitches 3| and 32. Switches 31 interposed in the conductors 35 and 38and actuated by c; ms 38 on the shaft 25 operate to interrupt theoperation of the motor 23 in opposite limit positions of the arm 2|.

The control system constituting the present invention operatesautomatically to detect deviations in the condition being controlledfrom a predetermined value, that is, the moisture content of the driedcloth and in response to such deviations to vary the position of theregulating device or arm 2| so as to maintain the controlled conditionaccurately and substantially at said value.

teristic of the web 5 which varies with the moisture content and byindicating deviations of this characteristic in opposite directions froma predetermined value corresponding to the moisture content desired tobe maintained. In the present instance, the alternating currentresistance of the web is the characteristic measured in order to avoidthe introduction of errors due to polarization, electrostatic charges,etc. The resistance measurement is made at a point beyond the outlet endof the drying chamber 1. For this purpose, the web passes between twoelectrodes 40 and 4|, one formed by the flat surface of a bar 42statlonarily mounted on the tenter frame. The other electrode comprisesa. plate supported by pivots 43 and urged downwardly toward the bar bygravity and a spring 44, The pivots are carried by a bracket 45supported by and insulated from the tenter housing.

The electrodes 40 and 4| with the variable cloth resistance therebetweenare interposed in an electric circuit, and variations in voltage dropthrough the cloth resulting from changes in cloth resistance areutilized through a suitable vacuum tube arrangement to actuate asensitive magnetic relay 46 by which selective operation of the controlswitches 3| and 32 is governed and the speed of the web driving motor I!is varied. Preferably, the relay 46 is of the galvonometer typecomprising a rotor 41 carrying a winding 48 and an arm 48 on which thecontact 33 of the control switches is mounted. The rotor 41 is pivotallysupported between the poles 58 of a permanent magnet and a return springis provided so that when the rotor winding is energized to apredetermined degree, the contact 33 will balance between thecooperating switch contacts, both control switches then being open. Asthe current rises above this predetermined value, the switch 3| will beclosed. The switch 32 is closed in response to a fall in the relayenergizing current.

To impress a voltage upon the cloth sample, the electrodes 40 and 4| areconnected across the terminals or a section 52 of a potentiometer 53 andin series with an adjustable rhcostat 54 and Detection of suchdeviations is eflected by continuously measuring an electrical characacontrol switch 55 having normally closed contacts 56 and 51. The circuitextends from the electrode 4| through a conductor 58, the switch 56, aconductor 58, the rheostat 54,'a conductor 5|, the resistance section52, a conductor 82, the switch 51, a conductor 58 to the electrode .48.Current is supplied to the potentiometer 53 from a secondary winding 54of a transformer designated generally by the numeral 55. Primary winding65 of this transformer is supplied with alternating current from theregulated voltage source 21,

The voltage drop between the electrodes is used to vary the grid voltageof a three element vacuum tube 61 biased to act as a rectifying detectorso that in accordance with the well known characteristics of such tubes,the output current of the tube will be varied correspondingly, Currentfor heating the tube filament or cathode 88 is supplied from a secondarywinding 58 of the transformer. High potential current may beconveniently supplied to the plate 10 of the tube from a vacuum tubetype of half-wave rectifier i 'H whose output is applied to apotentiometer 18. Th rectifier tube embodies a cathode l2 supplied withheating current from a secondary winding 13 of the transformer andwaplate 14 having a high alternating current voltage applied thereto fromstill another secondary winding I5 of the transformer. Output leads l6and 11 of the rectifier are connected across the opposite terminals ofthe potentiometer 18, and a filter condenser 18 in shunt therewith aidsin smoothing out the current.

Section 8| of the potentiometer I8 is utilized to supply a negative gridbias to the grid 82 of vacuum tube 61. To this end, the terminal of anadjustable slider 88 by which the grid bias may be varied is connectedto the filament 88 of the vacuum tube while one 01' the potentiometerend terminals is connected to the grid 82 through a conductor 83, theelectrodes, the conductor 68, the switch 51, the conductor 62,- and aconductor 84. With this arrangement, variations in the potential dropbetween the electrodes 4|! and 4| caused by variations in the resistanceof the web will vary the peak grid voltage and therefore change theaverage output of the vacuum tube 61.

The output current is utilized to actuate the relay 45 and also a.milliammeter 85. The ammeter may be calibrated to indicate deviations ofthe moisture content of the cloth from a value desired to be maintained.The output circuit extends from the plate 18 through a. conductor 85, achoke 81, the meter 85, a conductor 88, the winding 48, a conductor 88,a rheostat 88, a conductor 8|, resistances 82 and 83 to the filament 68,The plate voltage is thus determined by the potential drop because theresistances 82 and 83. The choke 81 and a filter condenser 84 operate tosmooth out the plate current.

A testing circuit is associated with the electrodes 48 and 4| in orderto facilitate checking of the circuit condition. For this purpose,resistors 85 and are connected in series relation and arranged to besubstituted in the potentiometer circuit in place of the cloth sampleand therheostat 54. The resistor 85 is connected to the adjustablecontact of the potentiometer while the other resistor is connectedthrough a switch 81 and the conductor 82 to the other potentiometerterminal. The common-terminal of the resistors is grounded and connectedto the conductor 88 through a conductor 88 and a switch 88. By

opening the switches 56-and 51 and closing the switches 91 and 99, thecloth sample and the active portion of the rheostat 54 will be withdrawnand theresistors 95 and 95 introduced in the potentiometer circuit. Theresistors are of equal values so as to divide the voltage of thepotentiometer equally.

When a vacuum tube is replaced, when the characteristics of the tubechange, or for various other reasons, it becomes necessary to test andreadjust the control circuits. For this purpose, the switch 55 isactuated to introduce the resistances 95 and 99 in the control circuit.Then, by adjustment of the potentiometers 59 and 19, the circuits areconditioned for the flow of a predetermined normal current, for example,ten milliamperes in the plate circuit, this being indicated on theammeter 85. The switch 55 is next operated to reintroduce the rheostat54 and the electrodes 49 and H with the dried cloth therebetween. If thesame kind of cloth has been used previously, the setting of the rheostat54 for the maintenance of the desired moisture content using the fixednormal plate current will be known. Accordingly, the rheostat will beset in the known position and the tenter will be started and operatedunder the control of the automatic regulating system.

A diiferent procedure is followed when the cloth is of a new kind. Insuch a case, the rheostat 54 would, after preliminary conditioning ofthe circuits for the normal plate current, be set .a the maximumresistance position and the tenter started. With this setting, thelowest possible moisture content would be maintained. The setting of therheostat would be advanced periodically until the tenter operator findsby examination that the dried cloth is of approximately the desiredmoisture content. Then, the moisture content would be determinedaccurately and the rheostat 54 adjusted in the proper direction. Thisprocedure would be repeated until the setting of the rheostat formaintaining the precise moisture content is established.

The control circuits, when properly conditioned as above described,operate as follows: When the desired moisture content prevails, thevoltage drop through the cloth sample will be half that delivered by thepotentiometer 59 because with a resistance in the rheostat 54 greatenough to take approximately half of the voltage drop across the sampleand rheostat combined, the otherwise troublesome effect of thecapacitive reactance of the sample is negligible in so far as concernsits effect upon the voltage drop across the sample. The polarities andtube characteristics are such that the normal plate or output currentwill maintain the relay 45 in balanced condition, both control switches9| and 92 being open.

Now, assuming that the web becomes abnormally dry, the voltage dropbetween the electrodes will rise above normal resulting in aproportionate increase in the plate current of the vacuum tube andthereby causing the relay to close the switch 9|. This short-circuitsthe shading coils 29 causing the motor 29 to turn the rheostat arm 2I ina counter-clockwise direction so-as to increase the speed of the tentermotor I9. As a resuit, the drying capacity of the tenter is decreasedprogressively as long as the control switch '9I remains closed.Conversely, if the web becomes too wet, the voltage between theelectrodes falls below the predetermined normal value. The resultinglowering of the alternating current grid voltage reduces the plate oroutput current of the vacuum tube 51 thereby causing the relay 49 toclose the switch 92 which initiates operation of the motor 29 in adirection to turn the rheostat arm 2I clockwise so as to decrease thespeed 0! the web driving motor I9.

The action above described is characteristic of controls of theso-called floating type wherein the regulating device continues to movethroughout the duration of a deviation in the controlled condition fromthe value desired to be maintained. Where, as in the present instance,there is a substantial lag in the response of the medium beingcontrolled to a change in the position of the regulating device,over-correction is apt to occur especially when the deviations of thecontrol condition occur rapidly. To overcome this, the present inventioncontemplates adaptation of the control above described for operationwith a proportioning action so that the regulating device or rheostatarm 2| will assume definite equilibrium positions for each diiferentvalue of moisture content of the cloth. Preferably, this is accomplishedby varying the energization of the relay 49 progressively with changesin the position of the rheostat arm so that the relay will be balancedat a diiierent value of the plate current for each position of therheostat arm.

In the present instance, such variations are eifected by changing theresistance of a shunt arranged in parallel with the relay winding 49.The shunt is formed by a rheostat I99 having a resistance element I9Iwith one terminal I92 connected by a conductor I99 to the conductor 98.A contact arm I94 wipes across the resistance element I9I and isconnected by a conductor I95 to the arm I95 of a second or adjustingrheostat I9'I having a resistance element connected at one end to aconductor I98 which is joined to the conductor 9|. The resistanceelement III is carried by an insulating body I99 fast on the maincontrol shaft 25. To prevent interruption of the shunt in the event thateffective contact between the arm I94 and the resistance element I9I isinterrupted by foreign matter or the like, a conductor H9 is extendedfrom the conductor I95 to the terminal III of the resistance element.

With the shunt arrangement above described, the proportion of the outputor plate current which is shunted around the relay winding 49 will bedetermined by the position of the contact arm I94 with respect to therheostat terminal I92. As the shaft 25 and the resistance element I9Iturn clockwise in response to closure of the switch 92 following a risein moisture content above normal, the resistance of the shunt willincrease progressively thereby correspondingly increasing the currentthrough the reiay winding. This increase will partly counteract thecurrent decrease which caused closure of the control switch 92 so thatthe relay 49 will be restored to balanced condition and the motor 29stopped before the moisture content has been reduced to the desirednormal value. Similarly, reverse movement of the element I9I initiatedin response to a decrease in moisture content results in a decrease inthe shunt resistance causing the control swtch 9| to be opened beforethe moisture content has risen to its full value. As a result of suchautomatic shifting of the control point of the system (the moisturecontent which the automatic control mechanism maintains) with changes inthe position oi the rheostat arm 2|, the latter will assume differentequilibrium positions for each different value of moisture content.

The value of the resistance element IN is coordinated with theconstruction of the relay and other parts in a manner such that therange through which the control point will be shifted in the movement ofthe rheostat arm 2I throughout its full range will be as small aspracticable without the attendant danger of producing objectionablehunting. By adjustment of the rheostats 90 and I01, the arms of whichare connected by a shaft II2 so as to turn in unison, the range of shiftof the control point of the system may.

be varied as desired without affecting the ratio of current distributionbetween the relay winding 48 and the shunt in parallel therewith at thenormal or mid-position of the contact arm I04. That is to say, therheostat 90 always bears to the rheostat I01 the same ratio as thewinding 48 does to the rheostat I when the latter is in its normal ormid-position.

After full advantage has been taken of the proportioning action abovedescribed in repositioning the rheostat following a rapid change inmoisture content, it is desirable to condition the control for operationwith a floating action so as to thereafter effect an accuraterestoration of the controlled condition to the precise value desired tobe maintained. To this end, means is provided which operates in responseto a change in the effective control point of the automatic mechanism toeliminate this shift and restore the desired normal control point at arate substantially slower than that at which the shift is produced bythe proportioning action above described. Such readjustment continuesuntil the control point has been. restored precisely to the fixed valuecorresponding to the moisture content desired to be maintained.

In the present instance, the supplemental adjusting means includes amechanism for actuating the rheostat I00 to restore a predeterminedeffective value of the relay shunt. The contact arm I04 is fast on andinsulated from a shaft II3 carrying a gear II4 which meshes with apinion IIS on a shaft Ili carrying a pinion II1 which is normallycoupled to a gear I I 8 of a train II9 driven by a shaded pole inductionmotor I20. By proportioning the gearing or by adjusting the capacity ofa fluid pump 9* driven from one element of the gearing, the speed of themotor I20 is adjusted so that the shaft III operates at only a smallfraction, for example one-tenth, of the speed of the main shaft 25.

The motor I20 is of the same construction as the motor 23 having shadingcoils I2I and I22 connected respectively through conductors I23 and I24to arcuate segments I26 and I20 carried by the insulating disk I09. Thesegments are arranged in end-to-end relation and spaced apart at theiradjacent ends by a short insulating segment I21. Thus, the segmentsrotate with the resistance element IM and the shaft 25. A brush I28narrower than the segment I21 bears against the latter or one of thesegments I and I26 and is carried by an arm I29 fast on the shaft Ill. Aconductor I30 connects the brush to the other terminal of each of theshading coils I2I and I22. It will thus be seen that when the brush I 28engages the segment I21, both shading coils will be open-circuited andthe shaft III will remain stationary. When the segment I28 is engaged bythe brush, the coils I22 will be short-circuited and ment of the shaftwill result from engagement of the brush and the segment I20. The motorI20 thus controlled will cause the brush I28 to follow the movements ofthe rheostat arm 2| but at a substantially slower rate. Such followingcontinues until the brush has again moved to a position opposite thesegment I21 in the new position of the latter.

OPERATION In explaining the operation of the complete controlarrangement, it will be assumed that the control circuits are adjustedin the manner previously described for the maintenance of the desiredmoisture content, for example, six per cent. When this precise contentprevails, the parts will be positioned as shown in Fig. 4, the switcharm 49 being balanced between the stationary contacts under theprevailing degree of energization of the relay winding 48 and thesegment I21 engaging the brush I28.

If the moisture content falls rapidly, the relay switch 3| will beclosed and the shading coils 29 short-circuited. The motor 23 will startto turn the shaft 25 counter-clockwise operating the rl? eostat 20 toincrease the tenter motor speed at a relatively rapid rate. In thismovement, the resistance element IOI turns with the rheostat arm 2|causing the resistance of the relay shunt to be decreased progressively.The resulting decrease in the current energizing the relay winding 48 atthe prevailing moisture content of the cloth will continue until thebalanced current value has been attained, whereupon the control switch3I will be opened, and operation of the motor 23 interrupted. Thecontrol thus operates initially with a true proportioning action todecrease the drying capacity of the tenter at a relatively rapid rateuntil equilibrium has been established between this capacity asdetermined by the position of the rheostat arm 2I and the re-- ducedmoisture content.

In the initial movement of the resistance element IN, the segment I26will make contact with the brush I28 and will continue to move acrossthe latter a distance corresponding to the proportioning movement abovedescribed. The

resulting short-circuiting of the shading coils I22 starts the motor I20in a direction to turn the rheostat arm I04 and the brush I28counterclockwise so as to follow-up the previous movement of the segmentI21. Such movement of the arm I04 is in a direction to increase theshunt resistance and therefore the relay current, but its resultanteffect in further changing the position of the regulating arm 2I willdepend upon the manner in which the moisture content in the clothchanges following the initial increase in the speed of the tenter motor.

If, for example, moisture content of the cloth remains at the reducedvalue after the rheostat arm 2I has reached its new equilibrium positioncorresponding to the changed moisture content. the continuedcounter-clockwise movement of the brush I28 will increase the shuntresistance and therefore the relay current above the balance value, thecontrol switch 3I becoming closed. This initiates furthercounter-clockwise movement of the rheostat arm 2I to further decreasethe drying capacity of the tenter. Since the winding IOI moves fasterthan the brush I04, the net effect will be to decrease the relay currentand the switch 3| will again be opened after a short movement of therheostat arm. Thus, until the decreased capacity of the tenter becomeseflective in increasing the moisture content of the cloth, the relaycurrent will be increased and decreased alternately in different amountssuch that the rheostat arm will be advanced intermittently in adirection to increase the speed of the tenter motor.

Now, assume that the decreased drying capacity of the tenter has becomeeffective at the outlet end of the drying chamber and that the moisturecontent of the cloth is being increased at a rate slower than that atwhich the effective control point of the system is being restored bycounter-clockwise movement of the shaft H3. Under these conditions, theincrements of counterclockwise movement of the rheostat arm 2I willcontinue intermittently but will be or shorter lengths due to the factthat, following each closure of the relay switch 2|, less movement ofthe shaft 2| will be required in order to cause opening of the switch atthe increased moisture content. Thus, the rheostat arm 2| will continueto move intermittently in the counter-clockwise direction at an averagerate. determined by the difierence between the rate of decrease of therelay current in response to the increase in moisture content and therate of increase of the relay current by turning of the brush I.

If, on the other hand, the moisture content begins to rise and cause therelay current to increase at a rate greater than the corresponding rateof increase due to operation of the motor I2! but slower than the rateof shift during operation of the motor 23, the relay switch 32 willbecome cloud thereby short-circuiting the shading coils 30 andinitiating clockwise movement of the shaft so as to cause the dryingcapacity of the tenter to be increased. As an incident to this, theresistance element IIII turns clockwise causing the relay current to be,increased more rapidly than the current is being increased bycounter-clockwise movement of the brush I20. Therefore, the switch 32becomes opened and the motor 2! stopped momentarily. As this cycle isrepeated, the rheostat arm 2| will be moved intermi'ttently in adirection to increase the dryin capacity of the tenter, this being at anaverage rate correqaonding in magnitude to the amount 1 the rate ofmoisture content decrease exceeds the rate of adjustment by theauxiliary mechanism including the motor I20.

As a result of the above described action of the auxiliary adjustingmechanism after the decreased drying capacity has actually becomeeffective in increasing the moisture content of the cloth, the brush I28will be advanced toward the segment I21. Evenutally, it will engage thesegment when the moisture content has been re- 1 stored fully to thepredetermined desired value as evidenced by positioning of the switcharm ll between the stationary switch contacts at the time when the brushI20 contacts the segment I21. The operation of the motor I2! is thusinterrupted.

The'control operates in a similar manner in response to a relativelyrapid rise in moisture content above the desired value. Such a changecauses the switch 22 to be closed resulting in short-circuiting or theshading coils which initiates rapid movement of the rheostate operatingshaft 2B in the clockwise direction so as to increase the dryingcapacity of the tenter. In the initial movement, the segment I25 engagesthe brush I2l thereby short-circuiting the shading coils Hi to initiateoperation of the motor I20 in a direction to decrease the shuntreslstance and the relay current. For the reasons set forth above, therheostat arm 2I will continue to move intermittently in a clockwisedirection and at a slow average rate until the increased drying capacityof the tenter becomes eilective at the electrodes 40 and II. Then, theclockwise movement will continue or counterclockwise movement will begindepending on the rate at which the moisture content decreases relativeto the rate of decrease of the relay current by continued operation ofthe motor I20. Eventually, when the increased drying action has reducedthe moisture content of the cloth to the desired value and the controlmechanism has, by engagement of the brush I28 and the segment I21, beenrestored to .normal condition, movement of the shaft 25 will beinterrupted.

It will be seen from the foregoing that in response to a relativelyrapid moisture'content change of substantial magnitude, the controlfirst operates with a true proportioning action. That is to say, the arm2I is moved at a relatively rapid rate determined by the speed of theshaft 25 to a position corresponding to the magnitude of deviation inthe moisture content. As a result, the drying capacity of the tenter ischanged rapidly so that the amount of correction for the deviation willbe made at a rate proportional to the amount of the deviation. Thenafter equilibrium between the position of the rheostat arm 2I and thechanged moisture content has been established, the action of the controlis changed to that of the floating type.

That is to say, the rheostat arm 2I is permitted to move beyond saidequilibrium position at a substantially slower speed, and the dryingcapaci'ty of the apparatus is further changed in the same direction soas to eilect a restoration of the moisture content in the cloth to thedesired value. In other words, slow movement of the rheostat arm 2I inthe proper direction eontinues so long as any deviation in the moisturecontent of the cloth sample persists. Ii, however, such overrunning inthe position of the rheostat arm 2I beyond the equilibrium positionresults in a relatively rapid restoration of the moisture content afterthe changed rate of dry-.

ing capacity has become eiIective at the electrodes III and II, theadvance of the rheostat arm 2I is retarded. Or, in the event that-therate of correction exceeds a predetermined value governed by the speedof the shaft III, movement of the rheostat arm may actually be reversedwhile the deviation in moisture content still persists. In this way, thedesired floating type of correcting action is obtained without theattendant danger of producing objectional overrunning of the moisturecontent from the value desired to be maintained.

In response to gradual changes in moisture content, the present controloperates in the manner described above with a characteristic floatingaction, the arm 2I being advanced at a substantially continuous slowrate throughout the continuance of the moisture content deviation. Forexample, whenever the moisture con-- tent falls sufliciently to causeclosure of the switch ll, the shading coils 2! become short circuitedand counter-clockwise movement of the rheostat arm 2I is initiated. Thismovement is interrupted as soon as the relay current has been decreasedsufliciently to open the switch ll. Since the segment I2 will then be incontact with the brush I28, the motor I2. will operate in a direction toincrease the relay current and again eiiect closure of the switch SI. Inthis way, the rheostat arm 2| is advanced intermittently in a directionto decrease the drying capacity during the continuance of a fall inmoisture content below the desired value. The average rate of thiscorrecting movement will, for the reasons set forth above, vary with themanner in which the moisture content deviates.

Experience has shown that by adjustment of the speed at which therheostat arm I04 is restored to its normal position, the number ofoperations of the motor 23 required in order to readjust the tentermotor speed following a deviation of the moisture content from thedesired control point may be reduced. Such variation in motor speed maybe effected by adjustment of the pump I I9'-.

Considering the mode of operation above described, it will be seen thatthe present control adapts itself automatically'to changes in thecharacter of the conditioning demand and operates in a manner mosteffective for accurate maintenance of the moisture content.

Auxiliary controls Provision is also made for disabling the automaticcontrol and adapting the rheostat actuating motor 23 for manual controlas is frequently necessary in the operation of a conditioning apparatussuch as the tenter above described. During manual control, however, thecondition of the automatic control mechanism is not changed in order tofacilitate automatic reestablishment of the controlled condition -uponreverting to automatic control.

To the foregoing ends, the application of current to the tenter motor I3is controlled by switches I3I and I32 which are held closed when a relayI33 is energized. This is effected by closure of a push button startswitch I34 which is interposed in a conductor I34 connecting the relaywinding to the direct current power lines, the winding being heldenergized by a locking circuit including a normally closed stop switchI36 and a switch I35 which is closed when the relay is energized. Ifdesired, a motor starting mechanism of any well known construction maybe interposed between the tenter motor and its control switches I 3| andI 32.

Whenever the tenter motor is energized, a relay winding I 31 connectedin parallel with the motor is energized and a switch I38 thereby heldclosed. The latter switch controls a locking circuit for the winding I39of a relay I40. This circuit extends from one alternating current powerline through a conductor I, the winding I39, a conductor I 42,'a lockingswitch I43 which is closed when the relay I40 is energized, a conductorI44 in which the switch I38 is interposed, a switch I45 having a movablecontact arm I46 pivoted at I41 and a conductor I48. The relay windingI39 may be energized independently by closure of a manually operablepush button switch I49 interposed between con .luctors' I42 and I44.When the switch I45 is opened by movement of the arm I46 in eitherdirection away from the position shown in Fig, 4, the relay ing coils toa conductor I52 leading to the conductor 35. Similarly, by moving thearm I46 into engagement with contacts I53, a short-circuit will beestablished for the coils 30 including a conductor I54 leading to theconductor 30. Thus, by manipulation of the arm I46 and the push buttonswitches I34, I36, and I49, both manual and automatic controls may berendered operative selectively, the automatic control always beingdisabled automatically as an incident to rendering the manual controloperative.

To avoid disturbing the positions of the parts of the automatic controlmechanisms, particularly of the rheostat I00, during manual adjustmentof the tenter motor speed, provision is made for disabling the drivefrom the motor I20 and for locking the resistance element IOI to thecontact arms I04 and I29. To this end, the shaft H5 is supported in itsbearings for axial movement between the normal position shown and aposition in which the pinion I I1 is disengaged from the gear H8 and inmesh with a gear I56 fast on the disk I09. In this latter position, theshafts 25 and H3 are positively connected together through the medium ofthe shaft H5.

The two clutches thus formed by the pinion I ll cooperating with thegears H8 and I56 are controlled by a spring I51 acting in compression toshift the shaft II5 axially in one direction and a solenoid I50 actingon the armature I59 on the shaft. The energizing circuit for thesolenoid I50 extends through a switch I60 which is maintained open whenthe relay I40 is energized. When the relay is deenergized to adapt themechanism for manual control, the switch I60 closes thereby energizingthe solenoid to disengage the pinion II! from the gear H8 and in thesame movement of the shaft II5 to connect the shafts 25 and H3. Duringmanual adjustment of the tenter motor speed, the position of the contactarm I04 with respect to the resistance element IOI will not bedisturbed. When the automatic control is again restored, the solenoidwill become deenergized to again render the driv of the motor I20operative.

I claim as my invention:

1 A control system having, in combination, a regulating member, a poweroperator for moving said member at an approximate predetermined speed,automatic condition-responsi"e mechanism controlling the operation ofsaid operator and including an electrical device adapted to be variablyenergized to vary the effective control point of said mechanism, meansfor varying the energization of said device progressively with changesin the position of said member including two relatively movable elementsone movable in unison with said member, actuating means responsive torelative movement between said elements out of a predeterminedpositional relation in either direction to cause relative movementsbetween the elements to restore said positional relation but at a rateslower than said predetermined speed, manually operable means forcontrolling said operator independently of said mechanism, and meansoperating automatically as an incident to operation of said manuallyoperable means to disable said actuating means.

2. A control system ha ing, in combination, a regulating member, a poweroperator for moving said member at a predetermined speed, automaticcondition-responsive mechanism controlling the operation of saidoperator and including an electrical device adapted to be variablyenersized to vary the eiiective control point of said mechanism, meansfor varying the energization of said device progressively with changesin the position of said member including two relatively movable elementsone movable in unison with said member, a reversible actuator forrelatively moving said elements at a rate slower than said predeterminedspeed, means responsive to relative movement between said elements outof a predetermined positional relation in either direction to initiateoperation of said actuator in a direction to cause relative movementsbetween the elements to restore said positional relation, and meansoperable selectively either to connect said actuator to said elements orto cause the elements to move in unison with saidmember.

3. A control system having, in combination, a regulating member, a poweroperator for moving said member at a predetermined speed, automaticcondition-responsive mechanism controlling the operation 01' saidoperator and including an electrical device adapted to be variablyenersized to vary the effective control point of said mechanism, meansfor varying the energization of said device progressively with changesin the position of said member including two relatively movable elementsone movable in unison with said member, means responsive to relativemovement between said elements out of a predetermined pofltionalrelation in either direction to cause relative movements between theelements to restore said positional relation but at a rate slower thansaid predetermined speed, and selectively operable means for disablingsaid last mentioned means and connecting said elements together formovement in unison with said member.

4. A control system having, in combination, a

regulating member, a power operator for moving said member at apredetermined speed, automatic condition-responsive mechanismcontrolling the operation oi said operator and including an electricaldevice adapted to be variably energized to vary the eilective controlpoint of said mechanism, means for varying the energizetion of saiddevice progressively with changes in the position of said member, andselectively operable means i'or disabling said last mentioned means.

5. A control system having, in combination, a r

regulating member, a power operator for moving said member at apredetermined speed, automatic condition-responsive mechanismcontrolling the operation of said operator and including an electricaldevice adapted to be variably dition in a medium the electricalresistance of which varies with changes in said condition, thecombination of a regulating member movable varying distances in oppositedirections to increase and decrease the value of said condition, a pairof electrodes with said medium disposed therebetween, a vacuum tubehaving a grid and output circuit, a manually adjustable resistance, apair of resistors of predetermined relative resistances, an electricalcircuit, selectively operable means for interposing either saidresistors or said electrodes and variable resistance in said circuit,and means for impressing the voltage drop across one of said resistorsor across said electrodes onto said grid, means for indicating the valueof the current in said output circuit, and an electrical relayresponsive to deviations of the output current in opposite directionsfrom a predetermined value for controlling the direction and extent ofmovement of said member.

7. In a system for maintaining a uniform condition in a medium theelectrical resistance of which varies with changes in said condition,the combination of a pair of electrodes with said medium disposedtherebetween, a vacuum tube having a grid and output circuit, a manuallyadjustable resistance, a pair of resistors of predetermined relativeresistances, an electrical circuit, selectively operable means forinterposing either said resistors or said electrodes and variableresistance in series relation in said last mentioned circuit, and forimpressing the voltage drop across one of said resistors or across saidelectrodes onto said grid, and means for measuring the current in saidoutput circuit.

8. In a system for maintaining a uniform condition in a medium having anelectrical characteristic which varies with changes in said condition,the combination of a regulating member movable varying distances inopposite directions to increase and decrease the value of saidcondition, a vacuum tube having an input circuit, means variablyenergizing said circuit in accordance with variations in saidcharacteristic, an output circuit for said tube, a balanced electricalrelay energized in accordance with changes in the current in said outputcircuit and having an armature movable in opposite directions from aneutral position, means responsive to the opposite movements 01 saidarmature to cause movement of said member in corresponding directions, ashunt in parallel with said relay, mechanism operable to vary theimpedance of said shunt with the movements of said member, two rheostatsrespectively controlling the relay and shunt circuits, and means bywhichsaid rheostats may be operated in unison to vary the range ofmovement of said member in response to given variations of saidcharacteristic.

9. In a system for maintaining a uniform condition in a medium having anelectrical characteristic which varies with changes in said condition,the combination of a regulating member movable varying distances inopposite directions to increase and decrease the value of saidcondition, a vacuum tube having input and output circuits, a balancedelectrical relay energized in accordance with current changes in saidoutput circuit, control means actuated by said relay for determining thedirection and extent of movement of said member, means responsive tochanges in said electrical characteristic and controlling said inputcircuit, a variable impedance connected in parallel with said relay,mechanism operable to very the value 01' said impedance with themovements of said member whereby to position the member in proportion tothe magnitude of said characteristic, and manually adjustable means forvarying the range of proportioning action while maintaining a fixedratio between the current through said relay and impedance.

10. In a system for maintaining a uniform condition in a medium theelectrical resistance of which varies with changes in said condition,

the combination of a regulating member movable varying distances inopposite directions to increase and decrease the value of saidcondition, a power operator for actuating said member, a circuitenergized by alternating current, a pair of electrodes interposed insaid circuit and having said medium disposed therebetween, a vacuum tubehaving a grid and an output circuit, means for impressing the voltagedrop between said electrodes onto said grid, an electrical relayresponsive to deviations of the current in said output circuit andcontrolling said operator to vary the position of said member.

11. In a system for maintaining a uniform condition in a medium theelectrical resistance of which varies with changes in said condition,the combination of a regulating member movable varying distances inopposite directions to increase and decrease the value of saidcondition, an electrical circuit having therein a manually adjustablerheostat providing a variable resistance and a pair of electrodes withsaid medium disposed therebetween providing a second variableresistance, a vacuum tube having a grid and output circuit, means forimpressing the voltage drop across one of said resistances onto saidgrid, an electrical relay responsive to deviations of the current insaid output circuit in opposite directions from a predetermined value,and means controlled by said relay for varying the position of saidmember.

12. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of a regulating member movable varyingdistances in opposite directions to increase and decrease the value ofsaid condition, a vacuum tube having input and output circuits, abalanced electrical relay energized to a degree corresponding to thecurrent in said output circuit and having an armature movable inopposite directions from a neutral position to cause movement of saidmember in corresponding directions, means responsive to changes in saidelectrical characteristic for controlling said input circuit, a shunt ofvariable resistance connected in parallel with said relay, and mechanismoperable to vary the resistance of said shunt with the movement of saidmember.

13. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of-a regulating member movable varyingdistances in opposite directions to increase and decrease the value ofsaid condition, a balanced electrical relay having an armature movablein opposite directions respectively when the relay is energized aboveand below a predetermined degree, control devices actuated in saidopposite movements to cause movement of said member in correspondingdirections, means providing an electrical circuit ex-tenfing throughsaid medium and operating to measure said electrical characteristic andto energiie said relay correspondingly, and mechanism operatingautomatically in response to the resulting movement-s of said member tochange the degree of energization of said relay in a reverse directionuntil said predetermined energization has been reestablished.

14. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of a regulating member movable varyingdistances in opposite directions to increase and decrease the .value ofsaid condition, a vacuum tube having input and output circuits, a relayenergized in accordance with current changes in said output circuit andhaving an armature movable in opposite directions from a, neutralposition to cause movement of said member in corresponding directions,means responsive to changes in said electrical characteristic forcontrolling said input circuit, an impedance in parallel with saidrelay, and mech anism operable to vary the value of said impedanceautomatically w th the movements of said member.

15. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of a regulating member movable varyingdistances in opposite directions to increase and decrease the value ofsaid condition, an electronic device having input and output circuits, arelay variably energized in response to current changes in said'outputcircuit and having an armature movable in opposite directions from aneutral position, a power operator responsive to such movement of saidarmature to cause movement of said member in corresponding directfons,means responsive to changes in said electrical characteristic forcontrolling said input circuit and thereby producing amplified changesin the output current, mechanism actuated automatically in unison withthe movements of said member and operating to change the energization ofsaid relay in a direction to restore said armature toward said neutralposition, and automatic means operating in response to movement of saidarmature out of said neutral position to'change the energization of saidrelay in the reverse direction but at a slower rate than the changeproduced by said mechanism.

16. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of a member movable varying distances inopposite directions to respuctively cause an increase and a decrease inthe value of said condition, a vacuum tube having input and outputcircuits, a relay variably energized in response to current changes insaid output circuit and having an armature movable in oppositedirections from a neutral position, a power operator responsive toopposite movement of said armature and operable to cause movement ofsaid member in corresponding directions, means responsive to changes insaid electrical characteristic for controlling said input circuit andthereby producing amplified changes in the output of said tube,mechanism actuated automatically with the movements of said member inresponse to movement of said armature away from said neutral positionand operating to change the energization of said relay in a directionand by an amount sufllcient to restore said armature to said neutralposition.

17. In a system for maintaining a uniform condition in a medium havingan electrical characteristic which varies with changes in saidcondition, the combination of a regulating member movable varyingdistances in opposite directions to increase and decrease the value ofsaid condition, a vacuum tube having input and output circuits, anormally balanced relay variably energized in response to currentchanges in said output circuit, means responsive to conditions ofunbalance of said relay and operable to cause movement of said member ina direction correspending to the direction or unbalance, meansresponsive to changes in said electrical characteristic for controllingsaid input circuit and put current. and mechanism actuated automaticallyas an incident to movement of said member to change the energisati'on ctsaid relay in a direction to restore the balanw thereof.

18. In a system for maintaining a uniiorm condition in a medium thealternating current resistanceoif which varies with changes in saidcondition. the combination of a pair of electrodes with said mediumdisposed therebetween and in contact therewith; reginatin means (orvarying said condition; means for applying an alternating potentialacross said electrodes; means including a resistance, having a valuesubstantially equal to that of the medium between said electrodes whensaid condition is normal, connected in series relation with saidelectrodes across said potential source. whereby the voltage drop acrosssaid electrodes is rendered substantially independent of the capacitivereactance of the medium; and means or actuating said regulating means inresponse to the voltage drop across said electrodes to maintain saidcondition substantially constant.

19. In a system for maintaining a uniform condition in a medium thealternating current resistance of which varies with changes in saidcondition. the combination oi a pair of electrodes with said mediumdispom therebetween and in contact therewith; regulating means forvarying said condition: means for applying an aiternating' potentialacross said electrodes: means including a resistance, having a valuesubstantially equal to that o! the mediumbetween said electrodes. whensaid condition is normal. connected in series relation with saidelectrodes across said potential source, whereby the voltage drop acrosssaid electrodes is rendered substantially independent of the capacitivereactance oi the medium; a vacuum tube having a grid and output circuit;means tor impressing the voltage drop across said electrodes onto saidgrid: and means for actuating said regulating means in response to thecurrent in said output circuit for maintaining said conditionsubstantially constant.

AUSTIN S. NORCROSS.

e csn'rmcn'm or corinscnofi.

. evens ernoncnoss, n11; hereby certifieo that error appears inflqeprinted specification of um above mmhered potent requiringcorrection as follows: Pmgel, sec

end colmo llne l5, for the word "thougx" read -through--; page 2, secondcoiumo, line 60, for "because" read -acrosagpage 5, first column, line67f:' -"1heoaete" reed rheo st'gt ypage'l, second column, line 65,

claim 9, for "very! reed -vary-; p e.ge 8; first column, line 14,8, andsec- 0nd column, lines 51, claims l2, l5, andl respectively, for"movefleni! rear reino vement-a-q same page, first co1mnh,. 11ne 61,'c1a1m 15, for "electricev' read -e1ectric-- ;=an l that the said LettersPatent should-be reed with this correction therein that the sem mayconform to the record or the @m .11; the'ygterit Office,

si n and aeal'ed thia 22nd day of my", '4. 12. 19M.

- i llenry ven Aradale, -Act1ng Commissioner of Patents.

- CERTIFICATE or CORRECTION.

rateqcno: zgzhli-Jz. June 1o, 191 1.

- AUS'I'I N S..NORCROSS. lit-11a; hereby certifie q that error appearsin theprinted specification of tho above numbered patent requiringcorrection as follows: Pagel, sec- 02nd. colfim line l5, for tho word"thougi" read -throu@1--; page 2, saccbnd coi hmui, line 60, for"because" read -"-acro ca {page 5, first column, line 673I r 'rheoa-tto"regd '-+rheo st' agt--';.page 7, second column, line 65,

claim 9, for "very" road --vary--; pogo Biirst column, line 14.8, andsecond -colMn, lines gland 51, claims l2, l5, andl respectively, formoveinent. read --jno vmenta--; sam'o page, first oolmnfi,. line 61,-claiml5, for

"electri col' road --e1ectric-- ;=an i that the said Letters Patentshouldho reozi with this correction therein that the same may conform totho record r thecose =11; the 1 ate1it' Office,

Sign and aqal'ed thia 22m day of J1i1y', 12.191 1.

ge r van Arsdale -Acting Commissioner of Patents.

